1. Field of the Invention
The invention generally relates to an operating method for a memory unit, in particular, to an operating method for a non-volatile memory unit.
2. Description of Related Art
A non-volatile memory is a type of memory that retains information it stores even when no power is supplied to memory blocks thereof. The non-volatile memory may be classified into a read only memory (ROM), a one time programming ROM (OTP ROM), and a memory for multiple read and programming. Besides, as the fabrication process improves, the non-volatile memory could be implemented with the same process as a complementary metal oxide semiconductor (CMOS) device.
As the OTP ROM described above, the OTP ROM may be classified into a fuse type and an anti-fuse type. The fuse type OTP ROM is short before the fuse type OTP ROM is programmed, and it becomes open after being programmed. In the contrary, the anti-fuse type OTP ROM is open before being programmed, and it becomes short after being programmed. Besides, based on the fabrication process characteristic of the metal oxide semiconductor (MOS) device, the anti-fuse OTP ROM is fit to be implemented with the CMOS fabrication process.
Besides, a programming operation of the OTP ROM unit is based on the breakdown of the oxide layer of the gate to form a permanent conductance channel. Furthermore, the formed location of the permanent conductance channel will change with the variation of the processes. Therefore, an operating method of the OTP ROM unit now usually results in erroneous judgments and higher power consumption because of the different formed location of the conductance channel.